U.S. patent number 8,660,487 [Application Number 12/477,293] was granted by the patent office on 2014-02-25 for contactless data transmission.
This patent grant is currently assigned to Infineon Technologies AG. The grantee listed for this patent is Edmund Ehrlich, Matthias Emsenhuber, Walter Kargl. Invention is credited to Edmund Ehrlich, Matthias Emsenhuber, Walter Kargl.
United States Patent |
8,660,487 |
Kargl , et al. |
February 25, 2014 |
Contactless data transmission
Abstract
A contactless device having an energy antenna configured to
transmit/receive an energy signal; and a data antenna configured to
transmit a data signal. Also, a method for transmitting a
contactless signal including transmitting/receiving an energy
signal from an energy antenna of a contactless device; and
transmitting a data signal from a data antenna of the contactless
device.
Inventors: |
Kargl; Walter (Graz,
AT), Ehrlich; Edmund (Graz, AT),
Emsenhuber; Matthias (Graz, AT) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kargl; Walter
Ehrlich; Edmund
Emsenhuber; Matthias |
Graz
Graz
Graz |
N/A
N/A
N/A |
AT
AT
AT |
|
|
Assignee: |
Infineon Technologies AG
(Neubiberg, DE)
|
Family
ID: |
43216142 |
Appl.
No.: |
12/477,293 |
Filed: |
June 3, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20100311328 A1 |
Dec 9, 2010 |
|
Current U.S.
Class: |
455/41.2;
340/10.3; 340/10.1; 343/741; 340/572.1; 320/137; 235/492; 343/866;
340/10.34; 235/439; 340/10.5; 235/451; 343/742 |
Current CPC
Class: |
H04B
5/0031 (20130101); H01Q 1/2216 (20130101); H04B
5/0087 (20130101); G06K 7/0008 (20130101); H04B
5/0037 (20130101); G06K 7/10217 (20130101); H02J
50/80 (20160201); H01Q 1/2225 (20130101); H01Q
21/28 (20130101); H02J 50/12 (20160201); H04B
5/0062 (20130101) |
Current International
Class: |
H04B
7/00 (20060101) |
Field of
Search: |
;455/41.2
;235/439,451,492 ;320/137 ;340/10.1,10.3,10.34,572.1,10.5
;343/742,741,866 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 466 949 |
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63-502394 |
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JP |
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4-500896 |
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JP |
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7-131376 |
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JP |
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09-073524 |
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Mar 1997 |
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JP |
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9-98014 |
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Apr 1997 |
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JP |
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09-321652 |
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Dec 1997 |
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JP |
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10-145443 |
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May 1998 |
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JP |
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11-039441 |
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Feb 1999 |
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JP |
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11-298368 |
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Oct 1999 |
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JP |
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2007-110577 |
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Apr 2007 |
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JP |
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WO-87/04865 |
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Aug 1987 |
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WO |
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WO-91/01531 |
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Feb 1991 |
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WO |
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WO-2006/109701 |
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Oct 2006 |
|
WO |
|
Primary Examiner: Gonzales; April G
Attorney, Agent or Firm: Schiff Hardin LLP
Claims
What is claimed is:
1. A contactless device, comprising: an energy antenna configured
to transmit/receive a non-data modulated energy signal only; and a
data antenna configured to transmit a data signal at a
substantially similar carrier frequency as the as the non-data
modulated energy signal, thereby resulting in a superposition of
the data signal and the non-data modulated energy signal.
2. The contactless device of claim 1, wherein the energy antenna is
a narrowband antenna.
3. The contactless device of claim 1, wherein the data antenna is a
wideband antenna.
4. The contactless device of claim 1, wherein the energy antenna
comprises a resonant circuit having a high quality factor, and the
data antenna comprises a resonant circuit having a low quality
factor.
5. The contactless device of claim 1, wherein only the energy
antenna comprises a resonant circuit, and the resonant circuit has
a high quality factor and is matched to resonance.
6. The contactless device of claim 1, further comprising a
modulator configured to generate the data signal using one of
ASK-modulation, PSK-modulation, FSK-modulation, QAM-modulation, and
DMT-modulation.
7. The contactless device of claim 1, wherein the data antenna is
further configured to receive a load-modulated signal.
8. The contactless device of claim 1, wherein the data antenna
comprises a voltage compensation source configured to compensate
for a voltage induced by the energy signal in the data antenna.
9. The contactless device of claim 1, wherein the energy antenna
comprises a voltage compensation source configured to compensate
for a voltage induced by the data signal in the energy antenna.
10. The contactless device of claim 1, wherein the energy antenna
and the data antenna are positioned with respect to one another
such that a voltage induced by the energy signal in the data
antenna is geometrically cancelled.
11. The contactless device of claim 1, wherein the energy antenna
and the data antenna are located in a same plane.
12. The contactless device of claim 1, wherein the contactless
device is a contactless reader.
13. The contactless device of claim 1, wherein the contactless
device is a contactless card.
14. The contactless device of claim 13, wherein the energy antenna
is configured to only receive the energy signal.
15. A contactless communication system comprising: a first
contactless device, comprising: an energy antenna configured to
transmit/receive a non-data modulated energy signal only; and a
data antenna configured to transmit a data signal at a
substantially similar carrier frequency as the as the non-data
modulated energy signal, thereby resulting in a superposition of
the data signal and the non-data modulated energy signal; and a
second contactless device configured to receive the superposition
of the energy signal and the data signal.
16. The contactless communication system of claim 15, wherein the
second contactless device comprises: a transmission antenna
configured to transmit a transmission signal; a pickup antenna
configured to receive the superposition of the energy signal and
the data signal transmitted from the first contactless device, and
the transmission signal; and a cancellation circuit configured to
subtract a voltage of the transmission antenna from a voltage of
the pickup antenna.
17. The contactless communication system of claim 15, wherein the
second contactless device comprises a single antenna configured to
receive a superposition of the energy signal and the data
signal.
18. A contactless device, comprising: an energy antenna means for
transmitting/receiving a non-data modulated energy signal only; and
a data antenna means for transmitting a data signal at a
substantially similar carrier frequency as the as the non-data
modulated energy signal, thereby resulting in a superposition of
the data signal and the non-data modulated energy signal.
19. A method for transmitting a contactless signal comprising:
transmitting/receiving a non-data modulated energy signal only,
from an energy antenna of a contactless device; and transmitting a
data signal from a data antenna of the contactless device at a
substantially similar carrier frequency as the as the non-data
modulated energy signal, thereby resulting in a superposition of
the data signal and the non-data modulated energy signal.
20. The method of claim 19, wherein the energy signal is a
narrowband energy signal, and the data signal is a wideband data
signal.
21. The method of claim 19, further comprising compensating for a
phase shift between the energy signal and the data signal.
22. The method of claim 19, further comprising generating the data
signal using one of ASK-modulation, PSK-modulation, FSK-modulation,
QAM-modulation, and DMT-modulation.
23. The method of claim 19, further comprising compensating for a
voltage induced by the energy signal in the data antenna.
24. The method of claim 19, further comprising compensating for a
voltage induced by the data signal in the energy antenna.
Description
BACKGROUND
The present invention is directed to a contactless communication
system having a high bit rate contactless data transfer.
FIG. 7 illustrates a known contactless communication system 700.
The basic components of contactless communication system 700 are
reader 710 and contactless card 720.
Reader 710 is also known as a Proximity Coupling Device (PCD).
Reader 710 includes generator voltage U.sub.0, transmission antenna
L.sub.PCD, resonance capacitor C.sub.res, and resistor R.sub.Q.
Transmission antenna L.sub.PCD and resonance capacitor C.sub.res
are configured to be in resonance, such that at a predetermined
frequency, only resistor R.sub.Q is seen from the perspective of
the generator voltage U.sub.0.
Contactless card 720 is also known as a Proximity Integrated
Circuit Chip (PICC), a smart card, a tag, a transponder, or a Radio
Frequency Identification (RFID) tag. Contactless card 720 includes
an inductive antenna L.sub.PICC, resonance capacitor C.sub.PICC,
and energy consuming resistor R.sub.PICC. Antenna L.sub.PICC and
resonance capacitor C.sub.PICC form a resonance circuit, and are
configured to provide contactless card 720 with a specific
resonance frequency.
In operation, transmission antenna L.sub.PCD transmits a carrier
signal, typically having a frequency of 13.56 MHz, which generates
a transmission field to supply the contactless card 720 with both
energy and data. Data can be transmitted to contactless card 720 by
modulation of the carrier signal. When contactless card 720
penetrates the transmission field of reader 710, the transmission
field induces a current in card antenna L.sub.PICC, and the
transmission antenna L.sub.PCD and card antenna L.sub.PICC are said
to be coupled. A voltage corresponding to the induced current is
then multiplied by the resonance circuit. In some implementations,
contactless card 720 is configured to transmit a response signal,
which is provided as the carrier signal with data modulated on a
subcarrier frequency, typically at a frequency of 848 KHz. The
response signal generates a response field that is detected by the
transmission antenna L.sub.PCD of reader 710.
In known systems such as contactless system 700, the communication
protocol between the reader and the contactless card may be defined
by any of numerous ISO (International Organization for
Standardization) standards, such as 14443 Type A/B, 18092, 15693,
18000, etc.
The data communication and energy supplied during downlink
communication from the reader 710 to the contactless card 720 is
accomplished with a single transmission antenna L.sub.PCD. To
optimize energy transfer and operating distance, the reader's
resonance circuit, comprising resonance capacitor C.sub.res and
transmission antenna L.sub.PCD, focuses on the carrier frequency
and is often designed to have a high quality (Q) factor. The
bandwidth is reciprocal to the Q factor, and thus the resulting
bandwidth is low. Also, a high Q factor resonance circuit will
attenuate the data-modulated carrier signal and affect the settling
time of the signal. For standardized data rates (such as up to 848
kbit/sec), the downlink bandwidth of reader 710 is adequate to
fulfill the transmission requirements. Higher data rates (such as
above 848 kbit/sec) demand a larger bandwidth but without reduction
of quality factor Q.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates a contactless communication system according to
an embodiment.
FIG. 1B illustrates a contactless communication system according to
another embodiment.
FIGS. 2A, 2B, and 2C illustrate signal diagrams of a superposition
of the energy signal and data signal resulting in the total
transmission signal of the reader according to respective
embodiments.
FIGS. 3A and 3B illustrate a contactless communication system
according to another embodiment.
FIG. 4 illustrates a contactless communication method according to
an embodiment.
FIG. 5 illustrates a contactless communication system according to
another embodiment.
FIG. 6 illustrates a contactless communication system according to
another embodiment.
FIG. 7 illustrates a known contactless communication system.
DETAILED DESCRIPTION
The present application is directed to a contactless communication
system and method of transmitting data between contactless devices
(e.g., a reader or contactless card) at high baudrates without
sacrificing communication quality.
The contactless device includes an additional transmission antenna.
The existing transmission antenna transmits/receives only an energy
signal. This existing antenna, referred to herein as an energy
antenna, has a resonant circuit with a high quality (Q) factor and
effectively a narrow bandwidth. Data transmission, on the other
hand, is accomplished using the additional antenna, referred to
herein as a data antenna, to transmit a data signal. Unlike the
energy antenna, the data antenna is a wideband antenna and is not
matched to resonance or matched with a low quality (Q) factor.
Signal suppression is used to cancel an influence of the signal of
each of the antennas on the other. This signal suppression can be
done geometrically or by using a voltage compensation source.
It is noted that some of the components of the embodiments shown in
the figures described below are also used in the known contactless
communication system 700 of FIG. 7. Accordingly, these components
are illustrated using the same or similar reference symbols. For
the sake of brevity, their descriptions will not be repeated for
each embodiment.
FIG. 1A illustrates a contactless communication system 100A
according to an embodiment.
As shown, contactless communication system 100A includes reader
110A and contactless card 120. Contactless card 120 is configured
the same as contactless card 720 described above with respect to
FIG. 7, and thus its description need not be repeated here.
Reader 110A includes an energy antenna L.sub.energy and data
antenna L.sub.data. When contactless card 120 is within the
transmission field of reader 110A, energy antenna L.sub.energy can
couple with card antenna L.sub.PICC at a coupling coefficient
K.sub.energy-PICC, and data antenna L.sub.data at a coupling
coefficient k.sub.data-PICC.
Energy antenna L.sub.energy has coupled thereto an energy generator
voltage U.sub.energy, resonance capacitor C.sub.res, and resistor
R.sub.Q1. Energy antenna L.sub.energy and resonance capacitor
C.sub.res are configured to form a resonance circuit, such that at
a predetermined frequency, only resistor R.sub.Q1 is seen from the
perspective of the energy generator voltage U.sub.energy. For
effective energy transfer, energy antenna L.sub.energy has a high
quality factor and thus a narrow bandwidth.
The data antenna L.sub.data has coupled thereto a data generator
voltage U.sub.data and resistor R.sub.Q2. Unlike energy antenna
L.sub.energy, data antenna L.sub.data is not coupled to a resonance
capacitor. Data antenna L.sub.data is typically located in a same
plane as energy antenna L.sub.energy, though it is recognized that
this is not necessarily required.
Signal suppression is used to cancel interactions between energy
antenna L.sub.energy and data antenna L.sub.data, that is to
prevent a voltage induced by an energy antenna signal in the data
antenna L.sub.data, and to prevent a voltage induced by a data
antenna signal in the energy antenna L.sub.energy. In the case of
FIG. 1A, this suppression is accomplished geometrically, that is
energy antenna L.sub.energy and data antenna L.sub.data are shaped,
sized, and positioned with respect to one another such that a
signal transmitted by one antenna is suppressed from inducing a
voltage in the other antenna. Signal suppression occurs when the
energy and data signals have the same amplitude but are in opposite
phase (i.e., a 180.degree. phase shift). When the contactless card
120 is not located near the reader 110A, there is substantially
complete signal suppression between energy antenna L.sub.energy and
data antenna L.sub.data. On the other hand, when the contactless
card 120 is located with the reader's 110A transmission field, the
only signal inducing a voltage in the L.sub.data antenna is that
from the contactless card 120.
In operation, energy voltage generator U.sub.energy generates a
voltage controlling energy antenna L.sub.energy to transmit an
energy signal to contactless card 120. For optimum energy transfer,
this energy signal is a narrowband signal, has a high quality (Q)
factor, and is focused at a carrier frequency. Unlike the
transmission antenna L.sub.PCD of the conventional system 700
described above with respect to FIG. 7, energy antenna L.sub.energy
transmits only energy and is not modulated with data.
Concurrently, data voltage generator U.sub.data generates a voltage
controlling data antenna L.sub.data to transmit a data signal to
contactless card 120, as will be described in further detail below.
This data signal is not influenced by a resonance circuit, and thus
the data signal can be wideband with little or no baudrate
limitation. The energy signal and the data signal are
superpositioned, that is geometrically added, in the air between
reader 110A and contactless card 120 to create the reader's total
transmission signal, as will also be described in further detail
below. This superposition concept is being described herein as
adding the energy signal and the data signal. It is appreciated,
however, that these signals represent magnetic fields generated by
currents in the respective antennas.
The energy antenna L.sub.energy has a resonance circuit, as
discussed above, and thus the energy voltage source U.sub.energy
and the energy antenna L.sub.energy are in-phase. In contrast, the
data antenna L.sub.data does not have a resonance circuit, and thus
there is a 90.degree. phase shift between data voltage source
U.sub.data and data antenna L.sub.data. The result is the energy
signal is in-phase and the data signal has a 90.degree. phase
shift. This phase shift between the energy and data signals can be
compensated for digitally in any known manner.
When contactless card 120 is moved within range of the reader's
total transmission signal, a current is induced in card antenna
L.sub.PICC. A voltage corresponding to the induced current is then
multiplied by the series resonant circuit, i.e., the card antenna
L.sub.PICC and the resonance capacitor C.sub.PICC. Contactless card
120 then transmits a response signal, which is a carrier of the
reader's total transmission signal with data actively modulated
thereon. The reader's data antenna L.sub.data detects the response
signal generated by the contactless card antenna L.sub.PICC.
FIG. 1B illustrates a contactless communication system 100B
according to another embodiment in which the transmission antenna
has a resonant circuit.
Contactless communication system 100B is similar to the contactless
communication system 100A of FIG. 1A, except that data antenna
L.sub.data has additionally coupled thereto resonance capacitor
C.sub.res2. Data antenna L.sub.data and resonance capacitor
C.sub.res2 form a resonance circuit, which has a low quality
factor. Since the data antenna L.sub.data of FIG. 1B has a
resonance circuit, the data voltage source U.sub.data and data
antenna L.sub.data do not have a phase-shift relative to one
another. The signals on the energy antenna L.sub.energy and the
data antenna L.sub.data are in-phase, and as a result, no phase
shift between the signals of the two antennas is required.
The other components of FIG. 1B are similar to the ones described
above with respect to FIG. 1A, and for the sake of brevity, their
descriptions will not be repeated here.
FIGS. 2A, 2B, and 2C each illustrate signal diagrams of a
superposition of the energy signal and data signal resulting in the
total transmission signal of the reader according to respective
embodiments.
FIG. 2A a signal diagram of a superposition of the energy signal
and data signal resulting in the total transmission signal of the
reader when the data signal is generated using phase-shift keying
(PSK) modulation performed by a modulator (not shown). PSK
modulation itself is known, and thus for the sake of brevity, its
details will not be included here.
The data antenna L.sub.data is configured to transmit a data
signal, and the energy antenna L.sub.energy is configured to
transmit an energy signal. A superposition (i.e., a geometrical
addition) of the data signal H.sub.data and the energy signal
H.sub.energy occurs "in the air," resulting in the reader's total
transmission signal H.sub.total. In mathematical terms,
H.sub.total=H.sub.energy+H.sub.data.
The energy signal H.sub.energy has a 0.degree. angle and a
predetermined amplitude. In FIG. 2A the energy signal H.sub.energy
is represented in the vector diagram by the horizontal, non-bold
vector, and in the signal diagram is represented by the dashed
wave.
The data signal H.sub.data is a 90.degree. phase-shifted signal,
and is modulated -90.degree. to represent a logic 0, or +90.degree.
to represent a logic 1. In the vector diagram the logic 1 (i.e.,
+90.degree.) for this signal is represented by the vertical,
non-bold, solid vector pointing upward, and the logic 0 (i.e.,
-90.degree.), is represented by the vertical, non-bold, dashed
vector pointing downward. In the signal diagram the data signal
H.sub.data is represented by the dotted wave. It is noted that if
no data is modulated onto the data signal, then there will be no
data signal, i.e., an amplitude of 0.
The superposition of the energy signal H.sub.energy and the data
signal H.sub.data in the air results in the reader's total
transmission signal H.sub.total. This total transmission signal
H.sub.total has a .+-.phi angle and a resulting amplitude. In the
vector diagram logic 1 (i.e., +90.degree.) for this signal is
represented by the bold, solid vector angled upward, and logic 0
(i.e., -90.degree.) is represented by the bold, dashed vector
angled downward. In the signal diagram the total transmission
signal H.sub.total is represented by the solid wave.
During transmission, if there is no modulation, the resulting
vector is that of the energy signal H.sub.energy because the vector
of the data signal H.sub.data is at 0 amplitude. After PSK
modulation begins on the data signal H.sub.data, the energy signal
H.sub.energy remains the same. To modulate the data signal
H.sub.data with a logic 1, the data signal is shifted +90.degree.
compared with the energy signal H.sub.energy. The solid vector of
the data signal H.sub.data points to logic 1, and the sum of the
vector of the energy signal H.sub.energy and the vector of the data
signal H.sub.data results in the vector of the reader's total
transmission signal H.sub.total, which again is the solid bold
vector.
Alternatively, if the data signal H.sub.data is modulated with a
logic 0, the data signal H.sub.data signal is changed such that
there is -90.degree. phase shift compared with the energy signal
H.sub.energy. The vector of the data signal H.sub.data then points
to the logic 0, and the vector of the energy signal H.sub.energy
plus the logic 0 vector of the data signal H.sub.data results in
the vector of the reader's data modulated transmission signal
H.sub.total pointing to the logic 0.
During a transition from logic 1 to logic 0, and from logic 0 to
logic 1, there is a 180.degree. phase shift. This can be seen in
the step of the signal timing diagram shown on the right half of
FIG. 2A.
FIG. 2B a signal diagram of a superposition of the energy signal
and data signal resulting in the total transmission signal of the
reader when the data signal is generated using amplitude-shift
keying (ASK) modulation. ASK modulation itself is known, and thus
for the sake of brevity, its details will not be included here.
The energy signal H.sub.energy has a 0.degree. angle and a
predetermined amplitude. In FIG. 2B, the energy signal H.sub.energy
in the vector diagram is represented by the horizontal, non-bold
vector, and in the signal diagram is represented by the dashed
line.
The data signal H.sub.data is a 0.degree. phase-shifted signal, and
is modulated with a particular amplitude and to 0.degree. to
represent a logic 1, or with a particular amplitude and to
-180.degree. to represent a logic 0. In the vector diagram the
logic 0 (i.e., -180.degree.) for this signal is represented by the
horizontal, non-bold solid vector pointing to the left, and the
logic 1 (i.e., 0.degree.) is represented by the horizontal,
non-bold dashed vector pointing to the right. In the signal
diagram, the data signal H.sub.data is represented by the dotted
wave.
Again, the superposition of the energy signal H.sub.energy and the
data signal H.sub.data in the air results in the reader's total
transmission signal H.sub.total. In the vector diagram logic 0
(i.e., -180.degree.) for this signal is represented by the bold,
solid vector, and logic 1 (i.e., 0.degree.) is represented by the
bold, dashed vector. In the signal diagram the total transmission
signal H.sub.total is represented by the solid wave.
During transmission, if there is no modulation, the resulting
vector is that of the energy signal H.sub.energy because the vector
of the data signal H.sub.data is 0 amplitude. After ASK modulation
begins on the data signal H.sub.data, the energy signal
H.sub.energy remains the same.
To modulate the data signal H.sub.data with a logic 0, the data
signal has a -180.degree. phase shift compared with the energy
signal H.sub.energy. The solid vector of the data signal H.sub.data
points to logic 0, and the sum of the vector of the energy signal
H.sub.energy and the vector of the data signal H.sub.data results
in the vector of the reader's total transmission signal
H.sub.total, which is the solid bold vector.
Alternatively, if the data signal H.sub.data is modulated with a
logic 1, the data signal H.sub.data signal is changed such that
there is 0.degree. phase shift compared with the energy signal
H.sub.energy. The vector of the data signal H.sub.data then points
to the logic 1, and the vector of the energy signal H.sub.energy
plus the logic 1 vector of the data signal H.sub.data results in
the vector of the reader's total transmission signal H.sub.total
pointing to the logic 1.
During a transition from logic 1 to logic 0, and from logic 0 to
logic 1, there is a 180.degree. phase shift. This can be seen in
the step of the signal timing diagram on the right half of FIG.
2B.
FIG. 2C a signal diagram of a superposition of the energy signal
and data signal resulting in the total transmission signal of the
reader when the data signal is generated using quadrature amplitude
(QAM) modulation. QAM modulation itself is known, and thus for the
sake of brevity, its details will not be included here.
As with the PSK and ASK modulation embodiments described above with
respect to FIGS. 2A and 2B, respectively, the superposition of the
energy signal H.sub.energy and the data signal H.sub.data in the
air results in the reader's total transmission signal
H.sub.total.
The energy signal H.sub.energy has a 0.degree. angle and a
predetermined amplitude. In FIG. 2C the energy signal H.sub.energy
is represented in the vector diagram by the horizontal, non-bold
vector, and in the signal diagram is represented by the dashed
wave.
The data signal H.sub.data is phase-shifted 135.degree. to
represent a logic 00, 45.degree. to represent logic 01, -45.degree.
to represent logic 10, and -135.degree. to 225.degree. to represent
logic 11. The vector of the data signal H.sub.data is a pure QAM
vector. The superposition of the H.sub.data vector and the
H.sub.energy vector results in the specific constellation diagram
shown in the vector diagram, with the reader's total transmission
signal H.sub.total being represented by the solid and dashed bold
vectors. In the signal diagram on the right, as with the signal
diagrams of FIGS. 2A and 2B, the data signal H.sub.data is
represented by the dotted line, the energy signal H.sub.energy by
the dashed line, and the total transmission signal H.sub.total by
the solid line.
The invention is not limited to PSK, ASK, or QAM modulation. Other
types of modulation, such frequency-shift keying (FSK) and Discrete
Multi-Tone (DMT), are possible. Also, the PSK and ASK modulations
are not limited to binary modulation, and the QAM modulation is not
limited to 4-QAM modulation.
In an embodiment, to detect the data signal H.sub.data, the energy
signal H.sub.energy can be measured and stored in contactless card
120. After modulation starts, the reader's total transmission
signal H.sub.total can be measured, and then the stored energy
signal H.sub.energy can be subtracted therefrom resulting in the
data signal H.sub.data. For QAM modulation, for example, if the
energy signal is subtracted from the total transmission signal, and
the result is represented as the known QAM modulation constellation
diagram having the first, second, third, and fourth quadrants of a
circle.
FIGS. 3A and 3B illustrate a contactless communication system
according to another embodiment having voltage compensation
sources. Contactless communication system 300 is similar to the
contactless communication systems 100A and 100B described above
with respect to FIGS. 1A and 1B, except that the signal suppression
used to cancel an influence of the energy signal on the data
antenna, and an influence of the data signal on the energy antenna,
is done electrically rather than geometrically.
Coupling between the L.sub.data antenna and the L.sub.energy
antenna is represented in FIG. 3A by coupling coefficient
k.sub.data-energy, and this coupling induces respective voltages,
U.sub.i-energy and U.sub.i-data, in the two antennas. Unlike the
embodiments shown in FIGS. 1A and 1B, the antennas of this
embodiment are not shaped, sized, and positioned in any particular
geometrical manner.
To suppress an influence of the energy signal on the data antenna
and the influence of the data signal on the energy antenna, two
voltage compensation sources are added. One compensation source,
U.sub.comp-data, compensates for the induced voltage U.sub.i-data
caused by the data signal H.sub.data in the energy antenna
L.sub.energy. The other compensation source, U.sub.comp-energy,
compensates for the induced voltage U.sub.i-energy caused by the
energy signal H.sub.energy in the data antenna L.sub.data.
FIG. 3B shows bar graphs illustrating this voltage compensation.
The bar graph on the left represents the energy antenna circuit.
Compensation source U.sub.comp-data compensates for the induced
voltage U.sub.i-data caused by the data signal H.sub.data, and the
result is the energy generator voltage U.sub.energy. The other bar
graph on the right represents the data antenna circuit.
Compensation source U.sub.comp-energy compensates for the induced
voltage U.sub.i-energy caused by the energy signal H.sub.energy
resulting in data generator voltage U.sub.data.
Electrical cancellation does not have a specific positioning
requirement for energy antenna L.sub.energy and data antenna
L.sub.data. It is preferable to not couple these two antennas well
with one another so as to not create induced voltages (i.e.,
U.sub.i-data and U.sub.i-energy) that are high. These antennas
should be positioned such that they each couple well to contactless
card antenna L.sub.PICC, and such that the induced voltages are at
a level that they can be compensated for electrically.
The other components of FIG. 3A are similar to the ones described
above with respect to other embodiments, and for the sake of
brevity, their descriptions will not be repeated here.
FIG. 4 illustrates a contactless communication method 400 according
to an embodiment.
During the contactless communication method 400, an energy signal
is generated, and a data signal is generated using a modulation
scheme, such as PSK, ASK or QAM modulation, at Step 410. If
necessary, a phase shift between the energy signal H.sub.energy and
the data signal H.sub.data is compensated for, at Step 420. The
energy signal H.sub.energy is transmitted/received from/to an
energy antenna L.sub.energy, at Step 430. The data signal
H.sub.data is transmitted from the data antenna L.sub.data, at Step
440. A voltage induced by the energy signal H.sub.energy in the
data antenna L.sub.data is compensated for at Step 450, and a
voltage induced by the data signal in the energy antenna
L.sub.energy is compensated for at Step 460. As discussed above, a
superposition between the energy signal H.sub.energy and the data
signal H.sub.data occurs in the air.
It is appreciated that this method is not limited to the specific
order of the steps shown in FIG. 4. Some of the steps may occur in
a difference order, or may occur concurrently.
FIG. 5 illustrates a contactless communication system 500 according
to another embodiment. Contactless communication system 500 differs
from the contactless communication systems of the embodiments
described above in that instead of the additional data antenna
being located in the reader, it is located in the contactless
card.
Contactless reader 510 is configured the same as contactless reader
710 described above with respect to FIG. 7, and thus its
description need not be repeated here.
Contactless card 520 includes energy antenna L.sub.PICC-energy and
data antenna L.sub.PICC-data. Energy antenna L.sub.PICC-energy in
contactless card 520 is a narrowband antenna as in the reader
implementation, and is coupled in parallel to capacitor
L.sub.PICC-energy and to resistor R.sub.PICC1. Unlike the reader
implementation, however, energy antenna L.sub.PICC-energy receives,
but does not transmit, energy. This is due to the fact that there
is no active source in contactless card 520 as there is in reader
510. Of course the application is not meant to be limited in this
respect as it is possible for contactless card 520 to include an
active source.
Data antenna L.sub.PICC-data is a broadband antenna for sending
and/or transmitting data. Data antenna L.sub.PICC-data has coupled
thereto a capacitor C.sub.PICC-data and a resistor R.sub.PICC2.
Data antenna L.sub.PICC-data and capacitor C.sub.PICC-data are
configured to form a resonance circuit having a low quality (Q)
factor. The modulated data can be generated by contactless card 520
actively (e.g., using PSK, ASK, or QAM modulation) rather than
using passive impedance modulation (i.e., backscatter or load
modulation) as done previously. Data antenna L.sub.PICC-data is
typically located in a same plane as energy antenna
L.sub.PICC-energy, though it is recognized that this is not
necessarily required. Also, it should be appreciated that the
particular circuit of the data antenna L.sub.PICC-data is merely an
example, and that an alternative circuit design, such as one that
does not include a resonance circuit, may be used.
The operation of contactless communication system 500 is similar to
that described above with respect to FIGS. 1A and 1B, and for the
sake of brevity, its description will not be detailed here.
The other components of FIG. 5 are similar to the ones described
above with respect to FIGS. 1A and 1B, and for the sake of brevity,
their descriptions will not be repeated here.
FIG. 6 illustrates a contactless communication system 600 according
to another embodiment.
Contactless reader 610 is configured the same as contactless reader
110A, 110B described above with respect to FIGS. 1A and 1B, and
thus its description need not be repeated here.
Contactless card 620 includes a separate pickup antenna
L.sub.pickup.sub.--.sub.PICC and a cancellation circuit 630 to
compensate for the card's transmission signal, which is generated
by a current in card transmission antenna L.sub.PICC. In operation,
the pickup antenna L.sub.pickup.sub.--.sub.PICC detects the card's
transmission signal together with the reader's total transmission
signal. The cancellation circuit 630 is configured to cancel the
card's transmission signal while maintaining the reader's total
transmission signal almost undistorted due to that fact that the
induced voltage of the reader's total transmission signal detected
by the separate pickup antenna L.sub.pickup.sub.--.sub.PICC is not
attenuated by the card's resonance circuit, which includes card
transmission antenna L.sub.PICC and card capacitor C.sub.PICC.
The specific details of cancellation circuit 630 are outside the
scope of this application, and for the sake of brevity, are not
included here.
The other components of FIG. 6 are similar to the ones described
above with respect to other embodiments, and for the sake of
brevity, their descriptions will not be repeated here.
In an alternative embodiment, any of the antennas, L.sub.energy and
L.sub.data, of reader 610 are modified to include a cancellation
circuit similar to that of contactless card 620. Again, the
specific details of such a cancellation circuit are outside the
scope of this application, and for the sake of brevity, are not
included here.
Although specific embodiments have been illustrated and described
herein, it will be appreciated by those of ordinary skill in the
art that a variety of alternate and/or equivalent implementations
may be substituted for the specific embodiments shown and described
without departing from the scope of the present application. This
application is intended to cover any adaptations or variations of
the specific embodiments discussed herein.
* * * * *